1. Field of the Invention
The present invention relates to a method and an apparatus for preventing corrosion of a contact, which can break an oxide coating produced on a contact of a switch, a connector, etc. by applying a large current, thereby preventing the contact from being corroded.
2. Description of the Related Art
As well known in the art, a contact of a switch, a connector, etc. is formed of a metallic material having high conductivity, so that small contact resistance is induced upon electrical connection. In the contact, under a non-connection state which corresponds to an off state, since a surface of the contacting portion is oxidized, contact resistance is likely to increase. Also, under a connection state, which corresponds to anon state, since a surface of a portion exposed around the contacting portion is oxidized, a produced oxide is likely to roll up toward the contacting portion to provoke fine sliding wear, which increases contact resistance. Although contact resistance of a contact increases due to oxidization, if a contacting state and a non-contacting state are appropriately repeated and a substantially large current is applied under the contacting state, the oxide can be removed through heating by current flow, whereby it is possible to prevent contact resistance from increasing.
In association with an input to an electronic apparatus, it is not necessary to always apply a large current capable of preventing corrosion to a contact. When the large current flows intermittently, malfunction may result from noise generation. Also, if the large current flows through the contact, a lifetime of the contact may be markedly shortened, or the contact is likely to melt. In order to cope with these problems, an apparatus for controlling a current of a contact has been disclosed in JP-A-Hei.2-297818, in which contact resistance of a contact is detected and, when the contact resistance is not less than a predetermined reference value, a large current is applied through contacts.
Also, a circuit for preventing corrosion of a switch has been disclosed in U.S. Pat. No. 5,523,633, in which when using a switch for a large current in a system having a low current level, such as an electronic unit, a large current is applied in the form of a pulse while a contact of the switch is turned on. Further, a contact signal discrimination device has been disclosed in JP-A-Hei.7-14463, in which a pulse-shaped corrosion-prevention current is periodically applied using charge and discharge to and from a condenser. Moreover, JP-A-2002-343171 has disclosed an apparatus for preventing corrosion of a contact of a switch, wherein a large current for preventing corrosion is applied for at least a predetermined holding time starting from a point of time the contact of the switch transits from an opened state to a closed state, and when the contact of the switch is in the opened state, impedance of an input signal line connected to the contact is decreased.